Research Report 2000 - MDC

Molecular Biology
and Genetics
of Cardiovascular
Diseases
Detlev Ganten
Analysis of complex
cardiovascular diseases
in the rat
The rat is one of the most important
model systems for complex, polygenic
diseases. Since all epidemiologically
important human diseases belong to
this category, the potential for major
advances through genetic
investigation is substantial.
In recent years we have demonstrated
that multiple chromosomal loci in rat
models contribute to blood pressure
regulation and hypertension.
Independent from elevated blood
pressure, additional genetic factors
contribute to end-organ damage and
stroke in these animals.
Ongoing research in our laboratory is
directed towards the identification of
the underlying predisposing genes and
the subsequent identification of their
molecular variants responsible for
different cardiovascular disease
phenotypes.
To localize disease genes within
chromosomal regions linked to
quantitative traits (e.g. blood
pressure), we are establishing multiple
congenic rat strains. These congenic
strains are being developed by
introgressing disease alleles
encompassing the quantitative trait
locus (QTL) into a non-affected
reference strain by successive
backcrossing and molecular analysis.
This strategy allows observation of
the effect and genetic analysis of a
single QTL. We are currently applying
this strategy to a number of QTLs for
blood pressure regulation, stroke, and
kidney disease in the stroke- prone,
spontaneously hypertensive, rat. A
similar strategy is currently being
adopted in collaboration with our
Israeli partners to elucidate the genetic
20
basis of salt-sensitive hypertension in
the Sabra rat model.
Combination of congenic
experimentation with the development
of subcongenic animals, having only a
fraction of the initial congenic
segment, will allow successive fine
mapping within a QTL.
Production and high throughput
characterization of genomic
resources for the rat genome
The ultimate identification of diseaserelevant
genes within QTLs by
positional cloning requires the
availability of a variety of genomic
tools, such as large insert genomic
library clones, cDNA libraries and
mapping ressources. As a partner in
national and international rat genome
projects, our group has produced
various genomic tools for the rat
genome, among them the first rat
YAC library, a high resolution
mapping cross, and a hybridizationbased
Interspersed Repetitive
Sequence (IRS-)PCR marker system.
A set of about 800 IRS-markers has
been assigned to rat genetic and
radiation hybrid (RH) maps. A
preliminary physical framework map
has been produced based on
hybridization data from this set of
markers against high density gridded
filters representing about 90.000 YAC
clones (corresponding to 20-fold
coverage) of the rat genome.
(for more details visit our webpage:
http://www.mdc-berlin.de/ratgenom/)
The mapping efforts of complex
cardiovascular traits by congenic
experimentation and positional
cloning will be used in ongoing
projects in combination with the
establishment of gene expression
signatures in target organs of congenic
animals and their parental progenitors.
High density arrays of cDNA clones
or gene-specific oligonucleotides are
used for this approach. A
combinatorial approach of positional
cloning and expression profiling will
provide a powerful tool to identify
potential candidate genes within
chromosomal regions for genetically
determined cardiovascular diseases.
Transgenic rat technology
In order to study the functional
relevance of genes linked to
hypertension and stroke, transgenic
rats are being produced with
alterations in the expression of these
genes. The power of this technology
has been demonstrated in several
transgenic rat models with
modifications in the renin-angiotensin
system. Rats expressing the mouse
renin-2 gene have helped in
understanding the physiological
functions of local renin-angiotensin
systems in tissues. Furthermore,
transgenic rats carrying the human
renin and angiotensinogen genes are
excellent models for studying
hypertension-induced end-organ
damage, particularly in the kidney. In
addition, numerous other transgenic
rat models for the study of
cardiovascular physiology have been
produced and analyzed in
collaboration with other groups.
Furthermore, transgenic technology in
the rat has been extended by the
generation of transgenic animals with
large genomic constructs and the
establishment of knockout technology
for this species.
Selected Publications
Bohlender, J., Menard, J., Edling, O.,
Ganten, D., and Luft, F.C. (1998)
Mouse and rat plasma renin
concentration and gene expression in
(mRen2)27 transgenic rats. Am. J.
Physiol. 274, H1450-H1456.
Hübner, N., Lee, Y.A., Lindpaintner,
K., Ganten, D., and Kreutz, R. (1999)
Congenic substitution mapping
excludes Sa as a candidate gene locus
for a blood pressure quantitative trait
locus on rat chromosome 1.
Hypertension 34, 643-648.
Yagil, C., Sapojnikov, M., Kreutz, R.,
Zurcher, H., Ganten, D., and Yagil, Y.
(1999) Role of chromosome X in the
Sabra rat model of salt-sensitive
hypertension. Hypertension 33, 261-
265.
Yagil, C., Sapojnikov, M., Kreutz, R.,
Katni, G., Lindpaintner, K., Ganten, D.,
and Yagil, Y. (1998) Salt susceptibility
maps to chromosomes 1 and 17 with
sex specificity in the Sabra rat model
of hypertension. Hypertension 31,
119-124.